No error when a function definition contains non-balanced braces

[Bugfire]

Sorry if I'm wrong in my understanding of the specs or where to report it.

The following code does not generate a parse error No error occurs on steep also.

RBS::Parser.parse_method_type("(foo: Integer]) -> Integer")

My repository for testing https://github.com/Bugfire/rbs-test/pull/1/checks

Thanks for the great Steep/RBS.